Base station, mobile station, and channel quality information reporting method

ABSTRACT

A channel quality information reporting method includes a setting step, wherein the number N of blocks for which the mobile station reports channel quality information among the M blocks is set in accordance with an amount of traffic; a reporting step, wherein the base station reports the number N of blocks to the mobile station; a receiving step, wherein the mobile station receives the number N of blocks from the base station; a selecting step, wherein the mobile station selects N pieces of channel quality information from M pieces of channel quality information corresponding to the M blocks; an averaging step, wherein the mobile station averages pieces of channel quality information excluding the selected N pieces of the channel quality information; and a reporting step, wherein the mobile station reports the N pieces of channel quality information and the averaged channel quality information to the base station.

TECHNICAL FIELD

The present invention relates to a base station, a mobile station, and achannel quality information reporting method, and specifically to atechnology for controlling the number of blocks with which channelquality information is reported when a system bandwidth is divided intoplural blocks.

BACKGROUND ART

In a mobile communications environment of HSDPA (High Speed DownlinkPacket Access), a base station (eNodeB) uses a Channel Quality Indicator(CQI) reported from a mobile station (UE) when scheduling radioresources for the mobile station. Specifically, the mobile stationreceives a pilot channel and the like from the base station, measuresquality information such as a Signal to Interference Ratio (SIR) (S1),and feeds back the CQI to the base station (S2), as shown in FIG. 1. Thebase station uses the CQIs reported from each mobile station and carriesout scheduling such as allocation of appropriate radio resources (See3GPP TS 25.214, “Physical layer procedures (FDD)”).

Typically, the CQI is 5-bit data. The mobile station can measure the CQIevery 2 ms. Therefore, the radio resource of 5 bits/2 ms=2.5 kbps isrequired for each mobile station in order to report the CQI, if themobile station reports the CQI at every measurement of the CQI.

SUMMARY OF INVENTION Problem to be Solved by the Invention

In a next generation mobile communications environment such as 3GPPEvolved UTRA and UTRAN, the base station can allocate for the mobilestation the resource blocks into which the system bandwidth is dividedin the frequency domain. Typically, a radio resource is divided into 24blocks in the frequency direction and into sub-frames of 0.5 ms as atransmission unit in the time direction, as shown in FIG. 2. The basestation needs to receive the CQIs corresponding to the resource blocksfrom the mobile stations in order to carry out appropriate schedulingwith respect to each resource block.

FIG. 3 shows a CQI report format and signal reception quality measuredat the mobile station. The signal reception quality measured at themobile station varies in the frequency direction. The mobile stationcalculates the CQIs corresponding to resource blocks from the signalreception quality, and produces the CQI report format from thecalculated CQI. For example, the CQIs are sorted in a block numberorder, and the CQI report format is composed of pieces of CQIinformation corresponding to the 24 blocks.

When it is assumed as above that the CQI is 5-bit data, the radioresource of 5 bit×24/0.5 ms=240 kbps is required for each mobile stationin order to report the CQIs. In this manner, when the system bandwidthis divided into the plural resource blocks, the amount of informationfor reporting the CQIs is increased.

The present invention has been made in view of the above, and isdirected to reduction of radio resources required for channel qualityinformation reported from a mobile station to a base station.

Means for Solving the Problem

The above objective of the present invention is achieved by a basestation that divides a system bandwidth into M blocks and allocates datato be transmitted to a mobile station for the divided blocks, the basestation comprising: an N setting portion that sets the number N of theblocks with which the mobile station reports channel quality informationamong the M blocks; and a control information generation portion thatgenerates control information for reporting the number N of the blocksto the mobile station.

In addition, the above objective of the present invention is achieved bya mobile station that communicates with a base station that divides asystem bandwidth into M blocks and allocates data for the divided blocksin order to transmit the data, the mobile station comprising: an Nreception portion that receives from the base station the number N ofthe blocks for which channel quality information is to be reported amongthe M blocks, the number N being set in accordance with an amount oftraffic; an N selection portion that selects N pieces of channel qualityinformation from M pieces of channel quality information that correspondto the M blocks; a remaining channel quality information averagingportion that averages pieces of channel quality information excludingthe selected N pieces of channel quality information; and a feedbackinformation generation portion that generates feedback information forreporting the N pieces of channel quality information and the averagedchannel quality information to the base station.

Moreover, the above objective of the present invention provides achannel quality information reporting method in a communications systemincluding a base station and a mobile station that communicates with thebase station, wherein the base station divides a system bandwidth into Mblocks and allocates data to be transmitted to a mobile station for thedivided blocks in order to transmit the data, the channel qualityinformation reporting method comprising: a setting step, wherein thenumber N of blocks for which the mobile station reports channel qualityinformation among the M blocks is set in accordance with an amount oftraffic; a reporting step, wherein the base station reports the number Nof blocks to the mobile station; a receiving step, wherein the mobilestation receives the number N of blocks from the base station; aselecting step, wherein the mobile station selects N pieces of channelquality information from M pieces of channel quality informationcorresponding to the M blocks; an averaging step, wherein the mobilestation averages pieces of channel quality information excluding theselected N pieces of the channel quality information; and a reportingstep, wherein the mobile station reports the N pieces of channel qualityinformation and the averaged channel quality information to the basestation.

Advantage of the Invention

According to an example of the present invention, the radio resourcesthat are required for the CQIs to be reported from the mobile station tothe base station can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing procedures of reporting quality informationfrom a mobile station to a base station.

FIG. 2 is a view showing a resource block into which a system bandwidthis divided in the frequency domain.

FIG. 3 is a view showing CQI report format and signal reception qualitymeasured at the mobile station.

FIG. 4A is a view showing an example of a relationship between signalreception quality measured by a mobile station and a CQI report format,according to an example of the present invention.

FIG. 4B is a view showing another example of a relationship betweensignal reception quality measured by a mobile station and a CQI reportformat, according to an example of the present invention.

FIG. 5 is a view showing a signal flow communicated between a basestation and a mobile station, according to an example of the presentinvention.

FIG. 6 is a block diagram of a mobile station according to an example ofthe present invention.

FIG. 7 is a block diagram of a base station according to an example ofthe present invention.

LIST OF REFERENCE SYMBOLS

-   -   10 mobile station    -   101 reception RF portion    -   103 CQI measurement portion    -   105 Best N selection portion    -   107 N reception portion    -   109 remaining CQI averaging portion    -   111 feedback information generation portion    -   113 transmission buffer    -   115 transmission signal generation portion    -   117 multiple combining portion    -   119 transmission RF portion    -   20 base station    -   201 reception RF portion    -   202 CQI reception portion    -   205 scheduler    -   207 N setting portion    -   209 control information generation portion    -   211 transmission buffer    -   213 transmission signal generation portion    -   215 multiple combining portion    -   217 transmission RF portion

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the drawings, an example of the present invention will bedescribed.

In the following example, it is assumed that a 5-bit CQI is used aschannel quality information reported from a mobile station (UE) to abase station (eNodeB), a system bandwidth is divided into 24 resourceblocks, and a sub-frame as a transmission unit of a radio frame is 0.5ms.

<CQI Report Format>

As stated above, when the CQI report format shown in FIG. 3 is used, theradio resource of 240 kbps is required for each mobile station. In thisexample of the present invention, the mobile station selects N CQIs inthe order of the decreasing signal reception quality (in the order ofthe decreasing CQIs). Regarding the selected N CQIs, the mobile stationreports the resource block numbers and the CQI values to the basestation. The remaining CQIs are averaged and the CQI report formathaving an information amount of N+1 CQIs is generated. By employing sucha report format, the information amount of the CQI report format isexpressed as {a·(N+1)+b·N}/(a·M), where a is the number of bits in theCQI, b is the number of bits required to discriminate the resource blocknumbers, and M represents the number of the resource blocks in onesub-frame. When the system bandwidth is divided into the 24 resourceblocks, b is equal to 5 because 5 bits are required to uniquely expressthe resource block number.

FIG. 4A shows the CQI report format in the case of N=6, and FIG. 4Bshows the CQI report format in the case of N=12. As shown, each CQI inthe CQI report format may be sorted in the descending order. In the caseof a=5, b=5, and N=6, the information amount of the CQI report format is65/120; and in the case of N=12, the information amount of the CQIreport format is 125/120. Namely, when N becomes 12 in the case of a=5,b=5, the reporting information amount is increased. However, in the caseof a=6, the information amount is reduced to 138/144. In such a manner,the maximum value of N that can reduce the information amount (referredto as Nmax, below) is limited depending on the values of a and b.Therefore, N may specifically take a value from zero to Nmax. Inaddition, when N is set to be Nmax+1, the mobile station may report theCQIs of all the M resource blocks.

The base station carries out scheduling in order to allocate theresource blocks taking account of the CQIs reported from the mobilestation. While various algorithms are conceivable as schedulingalgorithms, a resource block can be allocated to a user having thelargest CQI value among the CQIs reported for corresponding resourceblocks. Such a way of allocation is called MaxC/I. The resource blocksthat are excluded from the N CQIs and represented by the averaged valuecan be scheduled using the reported averaged value. MaxC/I cannotprovide fairness among users, while it is known that MaxC/I can maximizethroughput of the system. In order to provide the fairness among users,the CQIs reported for the corresponding resource blocks are convertedinto a metric of proportional fairness (PF), and a PF scheduling can beemployed. When providing service where a transmission delay is veryimportant as communications quality, the PF metric may be converted intoModified Largest Weighted Delay First (M-LWDF) or Exponential Metric,and scheduling may be carried out based on the M-LWDF or Exponentialalgorithm. Each one of these has quality where the resource block isallocated with high probability basically when the CQI is larger.Because radio transmission circumstances between the users subsequentlyindependently vary, when the CQI is larger (namely, when spontaneousradio channel conditions are better), the resource block is allocated,thereby dramatically improving radio transmission efficiency. Sucheffect is called multi-user diversity.

When these scheduling algorithms are employed, there is a tendency wherethe number of resource blocks to be simultaneously allocated isdecreased as the number of the users in the same cell is increased.Therefore, when there are a large number of the users in the same cell,it is more probable that reporting the M CQIs corresponding to theentire resource blocks results in reporting in vain. Namely, it isbeneficial to adjust the N value depending on the number of the users inthe same cell. By making the N value small when there are a large numberof the users and large when there are a small number of the users, theCQI reporting amount and the radio transmission efficiency can be keptin balance. However, because there are not always data to be transmittedto all the users, the N value may be adjusted taking the amount of datathat remains in a transmission buffer. The N value may be adjusted bymeasuring in the base station the degree of congestion, i.e., the amountof traffic, obtained by taking account of the number of the users, theamount of remaining data, and the like. Namely, the N value becomessmall when the amount of traffic is large, and the N value becomes largewhen the amount of traffic is small. The N value set by the base stationis adjusted for all the users through, for example, broadcastinformation. Alternatively, the N value is adjusted for an individualuser by taking account of required quality of the service for the user.For example, the N value becomes large for the user having a largeamount of data, and the N value may be small for a user having an amountof data small enough to empty the transmission buffer even when thenumber of the allocated resource blocks is decreased. The mobile stationfor which the base station specifies the N value selects the N resourceblocks whose CQIs are to be reported. In addition, regarding theresource blocks that are not selected within the N resource blocks, anaverage value is reported, thereby avoiding a problem in that there mayexist resource blocks that cannot be allocated by the scheduler.

The base station may average the number of blocks that are allocated ina recent frame for one user as a specific setting method of the N valuein order to obtain the N value. Here, an example is taken where 2resource blocks are allocated for a user A and 4 resource blocks areallocated for a user B in a previous sub-frame, and 4 resource blocksare allocated for the user A and 6 resource blocks are allocated for auser C in a second previous sub-frame. When the N value is calculatedusing the number of the resource blocks per user allocated in up to thesecond previous sub-frames, the N value becomes 4 from N=(2 blocks+4blocks+4 blocks+6 blocks)/the total number of the users (4)=4. Thecalculated N value may have a margin of α.

According to this example, because the base station specifies the Nvalue, i.e., the report format, the report format to be received by thebase station is specified in advance. Therefore, the base station can bein a standby mode with the specified report format.

<Signal Flow>

FIG. 5 shows a flow of signals communicated between the base station(eNodeB) and the mobile station (UE), according to the example of thepresent invention.

The base station analyzes the amount of traffic and comprehends thedegree of congestion (S101). When the amount of traffic is large the Nvalue is set small, and when the amount of traffic is small the N valueis set large (S103). The set N value is reported to the mobile station(S105).

When the mobile station receives a pilot signal or the like (S107), themobile station measures the CQI (S109). Next, the N CQIs are selected ina descending order (S111). The remaining CQIs are averaged (S113). Themobile station produces the CQI report format whose information amountcorresponds to (N+1) CQIs, and reports the same to the base station(S115).

When downlink data (DL data) to the mobile station are in the buffer(S117), the base station carries out scheduling so that a suitableresource block is allocated based on the CQIs reported from the mobilestation (S119), and transmits to the mobile station (S121).

<Mobile Station Configuration>

FIG. 6 is a block diagram of a mobile station 10 according to an exampleof the present invention. The mobile station 10 has a reception RFportion 101, a CQI measurement portion 103, a Best N selection portion105, an N reception portion 107, a remaining CQIs averaging portion 109,a feedback information generation portion 111, a transmission buffer113, a transmission signal production portion 115, a multiple combiningportion 117, and a transmission RF portion 119.

The reception RF (Radio Frequency) portion 101 receives a signaltransmitted from a base station, and separates signal components such asa pilot channel, a broadcast channel, and a control channel. Uponreceiving the pilot channel and the like, the CQI measurement portion103 measures a Signal to Interference Ratio (SIR) or the like, andgenerates a CQI. On the other hand, when the mobile station 10 receivesthe block number N of the blocks that report the CQIs, the block numberN is received by the N reception portion 107 through the reception RFportion 101. The Best N selection portion 105 selects the N CQIs amongthe M CQIs in descending order, the M corresponding to the number ofblocks that are measured by the CQI measurement portions 103. Theremaining (M-N) CQIs are averaged by the remaining CQI averaging portion109. The feedback information generation portion 111 generates the CQIreport format wherein the N CQIs and the averaged CQIs are combined. Asstated above, the CQI information amount is {a·(N+1)+b·N}/(a·M). Whenthe N value is greater than the threshold (Nmax), the feedbackinformation generation portion 111 may generate the CQI report formatthat reports the CQIs of all the M resource blocks.

The transmission buffer 113 stores user data to be transmitted from themobile station 10 to the base station. When user data are stored in thisbuffer, the transmission signal production portion 115 generates atransmission signal to be transmitted to the base station. The multiplecombining portion 117 multiplexes the CQI report format generated in thefeedback information generation portion 111 and the transmission signalgenerated in the transmission signal production portion 115, andtransmits the multiplexed signal to the base station through thetransmission RF portion 119.

<Base Station Configuration>

FIG. 7 is a block diagram of a base station 20 according to an exampleof the present invention. The base station 20 has a reception RF portion201, a CQI reception portion 203, a scheduler 205, an N setting portion207, a control information generation portion 209, a transmission buffer211, a transmission signal production portion 213, a multiple combiningportion 215, and a transmission RF portion 217.

The reception RF portion 201 receives a signal transmitted from themobile station and separates signal components from the received signal.When the base station 20 receives CQIs from the mobile station, the CQIsare received by the CQI reception portion 203 through the reception RFportion 201.

The scheduler 205 refers to Quality of Service (QoS) of user data storedin the transmission buffer 211 and/or takes account of an amount ofremaining data, thereby carrying out scheduling to allocate user datafor a suitable resource block.

As a result of this scheduling, a size (transport block size) of dataallocated for a resource block is specified to the transmission buffer211. In addition, the scheduler 205 reports allocation information andthe amount of traffic such as the amount of data remaining in thetransmission buffer to the N setting portion 207. The N setting portion207 controls the number N of the blocks for which the mobile stationreports the CQI, in accordance with the amount of traffic. As statedabove, when the amount of traffic is large the N value is decreased, andwhen the amount of traffic is small the N value is increased. Inaddition, the N setting portion 207 may set the N value for each mobilestation in accordance with service provided to the corresponding mobilestation. The control information generation portion 209 generatescontrol information for reporting the number N of the blocks to themobile station using the broadcast channel and the control channel.

The transmission buffer 211 stores user data to be transmitted from thebase station 20 to the mobile station. When user data are stored in thisbuffer, the transmission signal production portion 213 generates atransmission signal for transmitting user data having the data sizespecified by the scheduler 205 to the mobile station. The multiplecombining portion 215 multiplexes the control information (including thenumber N of the blocks) generated in the control information generationportion 209 and the transmission signal generated in the transmissionsignal production portion 213, and transmits the multiplexed signal tothe mobile station through the transmission RF portion 217.

As described above, according to the example of the present invention,the radio resources that are required for the CQIs to be reported fromthe mobile station to the base station can be reduced.

This international application claims the benefit of the priority dateof Japanese Patent Application No. 2006-169429 filed on Jun. 19, 2006,and the entire content of which application is herein incorporatedhereby by reference.

1. A base station that divides a system bandwidth into M blocks andallocates data to be transmitted to a mobile station for the dividedblocks, the base station comprising: a unit that sets, for each mobilestation, the number N of the blocks for which the mobile station reportschannel quality information among the M blocks such that the number Nincreases as an amount of data of the mobile station increases, whereinM is a positive integer greater than or equal to 2 and N is a positiveinteger; a control information generation portion that generates controlinformation for reporting the number N of the blocks to the mobilestation; a channel quality information receiving unit for receiving,from the mobile station, N channel quality information pieces, and anaverage value of channel quality information pieces other than the Nchannel quality information pieces; and a scheduling unit whichallocates a radio resource to the mobile station using the N channelquality information pieces, and the average value of channel qualityinformation pieces other than the N channel quality information pieces.2. The base station of claim 1, wherein the unit that sets N decreasesthe number N when an amount of traffic is large and increases the numberN when the amount of traffic is small.
 3. The base station of claim 1,wherein the unit that sets N averages the number of the blocks allocatedfor a predetermined period per one mobile station and calculates thenumber N.
 4. The base station of claim 1, wherein the unit that sets Nsets the number N depending on service provided for each mobile station.5. The base station of claim 1, wherein the unit that sets N increasesthe number N with respect to a mobile station when an amount of trafficallocated for the mobile station is large, and decreases the number Nwhen an amount of traffic allocated for the mobile station is small. 6.A mobile station that communicates with a base station that divides asystem bandwidth into M blocks and allocates data for the divided blocksin order to transmit the data, the mobile station comprising: a unitthat receives from the base station the number N of the blocks for whichchannel quality information is reported, which number N is set for eachmobile station, such that the number N increases as an amount of data ofthe mobile station increases, wherein M is a positive integer greaterthan or equal to 2 and N is a positive integer; a unit that selects Npieces of channel quality information from M pieces of channel qualityinformation that correspond to the M blocks; a remaining channel qualityinformation averaging portion unit that averages pieces of channelquality information excluding the selected N pieces of channel qualityinformation; and a feedback information generation unit that generatesfeedback information for reporting the N pieces of channel qualityinformation and the averaged channel quality information to the basestation.
 7. The mobile station of claim 6, wherein the feedbackinformation generation portion generates feedback information forreporting the M pieces of channel quality information corresponding tothe M blocks to the base station when the N is greater than apredetermined threshold.
 8. A channel quality information reportingmethod in a communications system including a base station and a mobilestation that communicates with the base station, wherein the basestation divides a system bandwidth into M blocks and allocates data tobe transmitted to a mobile station for the divided blocks in order totransmit the data, the channel quality information reporting methodcomprising: a setting step, wherein the number N of blocks for which themobile station reports channel quality information among the M blocks,such that the number N increases as an amount of data of the mobilestation increases, wherein M is a positive integer greater than or equalto 2 and N is a positive integer; a reporting step, wherein the basestation reports the number N of blocks to the mobile station; areceiving step, wherein the mobile station receives the number N ofblocks from the base station; a selecting step, wherein the mobilestation selects N pieces of channel quality information from M pieces ofchannel quality information corresponding to the M blocks; an averagingstep, wherein the mobile station averages pieces of channel qualityinformation excluding the selected N pieces of the channel qualityinformation; a reporting step, wherein the mobile station reports the Npieces of channel quality information and the averaged channel qualityinformation to the base station; a receiving step, wherein the basestation receives, from the mobile station, N channel quality informationpieces, and an average value of channel quality information pieces otherthan the N channel quality information pieces; and an allocating step,wherein the base station allocates a radio resource to the mobilestation using the N channel quality information pieces, and the averagevalue of channel quality information pieces other than the N channelquality information pieces.